Are our ideas about Dst correct?

The idea of two separate storm time ring currents, a symmetric and an asymmetric one has accepted since the 1960s. The existence of a symmetric equatorial ring current was concluded from Dst. However, the asymmetric development of the low-latitude geomagnetic disturbance ®eld during storms lead to the assumption of the real existence of an asymmetric ring current. I think it is time to inquire whether this conception is correct. Thus, I have investigated the development of the low-latitude geomagnetic ®eld during all the magnetic local times under disturbed and quiet conditions. The storm on February 6±9, 1986 and a statistical analysis of many storms has shown that the asymmetry does not vanish during the storm recovery phase. The ratio between the recovery phase asymmetry and the main phase asymmetry is low only for powerful storms. Storms of moderate intensity show the opposite. The global picture of the ®eld evolution of the February storm shows clear di€erences at di€erent local times. For instance the main phase and recovery phase start time does not coincide with Dst. Also the ring current decay is not the same at di€erent local times. Therefore, Dst gives an incorrect picture of the ®eld development. Moreover, asymmetry does not disappear during international quiet days as the investigation of the lowlatitude geomagnetic ®eld shows. Considering all these observations, I think we must revise our ideas about the ring current. In my opinion only one ring current exists and this is an asymmetric one. This asymmetry increases during storms and develops rather fast to more or less symmetric conditions. However, in no case is it justi®ed to conclude from Dst that a symmetric ring current exists.